A hypodermic syringe typically includes a generally tubular barrel portion, which may be formed of glass or plastic, a plunger having a stopper typically formed of an elastomeric material, such as rubber or synthetic rubber, and a needle cannula typically formed from an elongated tube having a fluid-conducting lumen. Such syringes may be prefilled with a medicament, drug or vaccine which require a shield or sheath enclosing the sharp end of the needle cannula typically formed of rubber or synthetic rubber. A needle shield includes an open end, a closed end, and a needle passage through the open end which receives the sharp end of the syringe needle cannula. As will be understood, hypodermic syringes must be sterilized prior to use by the healthcare worker or patient and such syringes are typically sterilized by the manufacturer and generally sealed in a plastic container ready for use.
A preferred method of sterilizing hypodermic syringes, particularly prefillable or prefilled syringes, is to “immerse” the syringe assembly in a sterilizing gas, such as ethylene oxide. Although there are several industry recognized methods of gas sterilization, such methods depend upon permeation of the sterilization gas into the passage of the needle shield to sterilize the syringe needle cannula. However, natural and synthetic rubber and vulcanizate thermoplastic elastomers are characterized as having a low gas permeability. Further, ethylene oxide gas, which is commonly used for gas sterilization. Alternatively, steam sterilization may also be used, but is generally limited to subsequent or “terminal” sterilization. As used herein, “sterilization gas” may be any gas used for sterilization, including ethylene oxide and steam. Therefore, the cycle time required for gas sterilization is relatively long. That is, the syringe is first immersed in the sterilization gas for a time sufficient for the gas to sterilize the syringe, including the needle cannula. Following sterilization, the sterilized syringes are “quarantined” for a time sufficient for the sterilization gas to escape, including any residual gas trapped in the needle shield. Thus, the sterilization cycle time is dependent in part upon how easily the gas penetrates through the needle shield during sterilization and removal of the gas from the syringe assembly. Tests are conducted to confirm that the sterilized syringe assemblies contain only minute traces of residual ethylene oxide or water in steam sterilization prior to release for distribution or sale.
A particular concern with the design of syringes is reduction of the needle cannula penetration force and patient comfort. The distal end or point of the needle cannula is typically provided with a tip geometry for piercing a patient's epidermis, flesh or tissue to deliver a fluid medicament, drug or vaccine stored or held in the syringe barrel. A healthcare worker or patient may also employ the syringe needle cannula to pierce an elastomeric septum or stopper of a vessel, such as a vial, to reconstitute dry or powdered medicament, drug or vaccine or to aspirate a liquid medicament, drug or vaccine contained in the vial.
Various considerations must be made when designing a syringe. For example, it is obviously desirable to minimize the needle cannula penetration force necessary for urging the needle cannula point or tip through the epidermis and flesh of the patient. It is generally believed that by reducing the needle cannula penetration force, the patient will perceive less pain. Another consideration in designing needle cannula point geometry is to prevent or minimize “coring”. Coring, as those skilled in this art understand, results when a portion of the material through which the needle cannula has penetrated becomes lodged in the lumen adjacent the needle cannula tip.
Various attempts have been made to reduce the required penetration force of syringe needle cannulas and reduce coring as discussed more fully in the above-referenced co-pending application. These efforts have been primarily directed to improving the design of the needle cannula tip by providing facets or bevels, for example, to reduce the required penetration force. Other attempts have been made to minimize the required penetration force by minimizing coring. However, these efforts have not been as successful as desired. Further, various efforts have been made to improve syringe needle cannula shields or sheaths, particularly for prefilled hypodermic syringes. Such improvements generally relate to protecting the needle cannula and preventing inadvertent coring of the needle shield by the needle cannula as disclosed, for example, in U.S. Pat. No. 4,964,866 assigned to the assignee of the present application, the disclosure of which is incorporated herein by reference. Further efforts have been made in the design of needle shields or syringes to reduce the gas sterilization cycle time by providing non-linear channels in the needle cannula shield which permit entry and egress of the sterilization gas while preventing entry of microorganisms.
However, no one has recognized the inter-relation between the selection of the material from which the needle shield is formed and the required penetration force of the needle cannula. The present invention relates to an improved five-beveled point geometry for a hypodermic needle and a needle shield which reduces the penetration force of the needle cannula. It is also believed that the improved needle shield will reduce gas sterilization cycle time.